Open-mouthed containers of plastic are widely used for packing beverage, food, medical supplies, and even cosmetics. The open-mouthed containers undergo the sterilization of their insides for germfree state before filling such items to be packed; thereafter they are filled with contents and then sealed. As an alternative to the sterilization of an open-mouthed container by chemical treatment, which requires a large-scaled facility, it has been used to sterilize the inside and the outside of such container by electron beam irradiation while transferring the container at a high-speed.
Explanations are provided hereunder referring to electron beam irradiation apparatuses that sterilize the insides and the outsides of open-mouthed plastic containers typically such as PET bottles.
For example, an electron beam irradiation device has been proposed in JP 10-268100A1 (Patent Literature 1). In that device, the inside and the outside of an open-mouthed container are sterilized with electron beam while the open-mouthed container is transferred through the irradiation area that has an electron beam generating means. While in movement, the open-mouthed container is turned from upright position to laid-flat position on its side and passes through the irradiation area rolling.
As another idea, a container sterilizer by means of electron beam has been proposed in JP11-1212A1 (Patent Literature 2). In that sterilizer, an electron beam generating means is arranged vertical-longitudinally in an electron beam irradiation area. An open-mouthed container is transferred into the irradiation area in upright position to be irradiated with electron beam generated from the electron beam generating means, in which the open-mouthed container is rotated so that the inside and the outside of the open-mouthed container will be sterilized while in movement.
Similarly, a sterilization method and apparatus of vessel has been proposed in JP2002-104334A1 (Patent Literature 3). In that method, an open-mouthed container is transferred into an irradiation area in upright position to be sterilized. The irradiation area is provided with one electron beam irradiation means, which emits electron beam. The electron beam emitted from the electron beam irradiation means is deflected by alternating-current magnetic field to scan in the direction of container transfer and is shared by radially arranged nozzles so that plural containers will be sterilized one by one with irradiation while traveling.
In the electron beam irradiation device described in Patent Literature 1 cited above, the open-mouthed container is transferred in upright position, but is temporary laid flat on its side while traveling through the irradiation treatment area. Therefore integrating this device into a production line requires the device to have a laying and raising mechanism. The mechanism, when integrated however, largely lowers the line speed for transferring the open-mouthed container. Thus, the integrating of the device is a hard problem for such a production line as is required to have high production efficiency in conveying open-mouthed containers.
In contrast, the electron beam irradiation apparatus described in Patent Literature 2 can be integrated into various production lines. In tinsidehis application however, the production line should run at a reduced conveying speed or should use a high-energy electron beam generating means to sterilize fully both the inside and the outside of the open-mouthed container. This is because of the fact that, in this container sterilizer, each of the open-mouthed containers on being carried is irradiated sideways for sterilization by a single electron beam irradiation window provided on the electron beam generating means in the apparatus as it passes the irradiation window.
Further, in the electron beam irradiation apparatus described in Patent Literature 3, the single electron beam generating means should have a number of nozzles arranged radially to share emitted electron beam to irradiate each of open-mouthed containers on being conveyed in series on a production line. This requirement results in a sophisticated apparatus structure. To sterilize fully both the inside and the outside of the open-mouthed container using the apparatus described in Patent Literature 3, the production line should run at a reduced conveying speed with a problem in the enhancement of the efficiency of the production line.
To improve these situations, the inventor of the present invention proposes an electron beam irradiation apparatus for open-mouthed containers having a configuration, in which a rotating body is provided rotatively in an irradiation processing chamber, plural retaining mechanisms are installed on the outside face of the rotating body at a regular interval, open-mouthed containers are held severally on the retaining mechanism, and thereby the open-mouthed containers are rotatively conveyed in a chain at a high-speed. In this apparatus, a predetermined area in the conveying path formed between the irradiation processing chamber and the rotating body is used as an irradiation area. Above the irradiation area, an electron beam generating means is arranged to emit electron beam, which irradiates the open-mouthed containers to sterilize.
In that electron beam irradiation apparatus for open-mouthed containers, the open-mouthed containers rotatively conveyed into the irradiation area in the irradiation processing chamber are sterilized by irradiation of electron beam passed through a small irradiation window provided on the top face of the irradiation processing chamber. Therefore, the exposure dose over the open-mouthed containers decreases if the emission holes of the grid plate of the electron beam source in the electron beam generating means and the irradiation window of the irradiation processing chamber, further and, the open-mouthed container are not inline, even very slight extent. In an extreme case, the irradiation efficiency of the open-mouthed container possibly drops below half.
In the electron beam irradiation apparatuses of this kind for open-mouthed containers, electron beam is emitted continuously from electron beam generating means. Therefore, if alignment deviates from the correct positioning as stated above, the irradiation hits not only the open-mouthed containers facing the irradiation window but possibly hits also the outsides of open-mouthed containers adjacent to the target containers causing an over-dose of electron beam irradiation of the adjacent containers.
To prevent undesired irradiation of the open-mouthed containers other than intended irradiation target, it is necessary to provide some contrivance such as widening the interval of the retaining mechanisms on the rotating body and providing an electron beam shield on each of the retaining mechanisms to limit the electron beam exposure area.
These contrivances however increase dimensions of the rotating body and the irradiation processing chamber; and further, it makes the capacity of the power supply unit of the electron beam generating means large. Therefore, an electron beam irradiation apparatus intended for incorporating in a production line that conveys open-mouthed containers at a high-speed has encountered a problem of growth in overall size that prevents economical manufacture of the apparatus.
An object of the present invention is to provide such an electron beam irradiation apparatus for open-mouthed containers as offers greatly improved electron beam irradiation efficiency with efficient sterilization of open-mouthed containers and economized manufacturing by virtue of its downsized feature.